Prior electro-stereoscopic video cameras described in the literature are of the type discussed by U.S. Pat. No. 4,583,117, to Lipton, et al., or the type described by U.S. Pat. No. 4,879,596, to Miura, et al. In the former case, two individual video camera heads (consisting of lenses and image sensors) are used, mounted on a base, to provide the two perspective viewpoints. In the latter disclosure, two video cameras are used, but packaged in a more pleasing manner to provide the appearance of an integral camera. In both cases, two sets of lenses and image sensors are employed, and in both cases, the image is displayed field-sequentially so that left and right perspective viewpoints are alternated. When viewed through shuttering devices each eye sees only its appropriate perspective viewpoint, and the result is an image perceived with the depth cue stereopsis.
Electronic stereoscopic video cameras have been sold for applications such as teleoperations using the field-sequential approach, following the art taught in U.S. Pat. Nos. 4,583,117 and 4,523,226 [both Lipton et al.] and for amateur applications the above referenced U.S. Pat. No. 4,879,596 [Miura et al.] has been recommended. In addition, systems using the technology described in U.S. Pat. No. 4,562,463 [Lipton] have been demonstrated at various trade shows.
In the case of U.S. Pat. No. 4,523,226 and the related U.S. Pat. No. 4,583,117, flickerless images result, but each eye will see an image with half the number of video lines which can be displayed in the planar image using the same bandwidth. The restoration of the full complement of lines per eye is achieved with image storage, using devices called scan converters or line doublers available from JVC, Sony, Macrodata, and others.
The technology described in U.S. Pat. No. 4,562,463 can produce a flickerless effect while maintaining the full complement of lines for each eye by storing the scanned video fields and playing back each field twice, at twice the vertical rate at which it was read.
Both of these means are upwardly compatible with regard to the existing video infrastructure. That is to say, for NTSC, PAL, or SECAM video, the image may be transmitted or stored using unmodified hardware.
A number of proposals have been made with regard to selection devices employed for the display of such images. Two such proposals by Lipton et al., in U.S. Pat. Nos. 4,792,850 and 4,884,876, describe respectively means using passive and active eyewear. Products using the art described in these two patents have been manufactured by StereoGraphics Corporation, and are in use by persons in fields such as molecular modeling, aerial mapping and for various other applications. The technique described in U.S. Pat. No. 4,523,226, mentioned above in the context of video systems, has proved to be a cost effective means for formatting flickerless computer generated images for stereoscopic display from unmodified computer hardware.
In the past few years, a number of people have begun to use electronic stereoscopic displays for computer graphics. On the other hand, the field of stereoscopic television and video cameras has lagged behind, in part because there are no integral camera units which can meet the performance standards set in the field of electro-stereoscopy for computer graphics.
The only integral stereoscopic video camera is one which was produced under U.S. Pat. No. 4,879,596 to Miura et al. ("Miura"). However, the convergence technique described in Miura will create images that have geometric distortion. FIG. 1 (taken from Miura) shows the arrangement used for converging the lenses on a subject which is to appear in the plane of the display screen. Such a rotation of the lenses and image sensors must always result in geometric distortion as illustrated in FIGS. 2a and 2b. It has been understood in the literature of stereoscopy that such rotation will create what is sometimes called "keystoning". This is a geometric distortion with a resultant misalignment of corresponding points in the vertical direction, producing undesirable vertical parallax.
Rotation of the rectangle shown in FIG. 2a about the dotted line representing a vertical axis will result in an apparent change in the length of the vertical sides AC and BD, resulting in a longer side A.sup.1 C.sup.1 and a shorter side B.sup.1 D.sup.1, as shown in FIG. 2b. This rotation is the geometric equivalent of that which is produced by the rotation of the camera heads shown in FIG. 1. When viewing such an image stereoscopically the eyes will be called upon to fuse corresponding image points with vertical parallax. The eyes are not called upon to do this when looking at objects in the visual world and the effort of fusing images with vertical parallax uses the muscles of the eyes in an unusual manner. Most people will experience this as a source of discomfort.
When the video camera heads, lenses and sensors, are rotated as called for by Miura, this is the result, and the geometric distortion is especially serious for objects which are close to the lenses or if wide angle optics are employed. This phenomenon is described in a paper by John Baker ["Generating Images for a Time-Multiplexed Stereoscopic Computer Graphics Systems," Proceedings of the SPIE-ISOE, Vol. 761, 1987]. Baker discusses the cure for the distortion, namely the use of cameras with parallel lens axes, and accomplishing convergence through horizontal shifting of left and right image fields. This technique is also given in Lipton's U.S. Pat. No. 4,523,226.
The means set forth herein for preventing the occurrence of geometric distortion in video camera produced images may also be used to produce superior results when applied to the elimination of the generation of spurious parallax due to recentration of zoom lenses, described by Lipton in U.S. Pat. No. 4,418,993.
In some conventional rangefinding techniques, signals from a pair of laterally separated radiation sensors are compared electronically to compute the distance to a sensed object in a direction perpendicular to the plane of the sensors.
A similar technique is described in U.S. Pat. No. 4,751,570 to Robinson, for controlling the convergence (and other parameters) of a stereoscopic video camera for the purpose of improving image quality. In the Robinson system, convergence is controlled by rotating the left and right camera heads. Robinson suggests that range information can be provided by transmitting laser or ultrasound radiation to an object, and detecting and processing reflections of the radiation in a programmed microcomputer to generate control signals for setting such camera parameters as the relative rotational orientation of the camera heads.
However until the present invention, no stereoscopic video camera had been developed which generated control signals for controlling camera convergence, zero parallax setting, or recentration, by processing signals representing the camera's normal, unmodified left and right image fields to generate control signals for adjusting the effective position of the left and right sensors in relation to fixedly mounted camera lenses. The invention eliminates the need to transmit a special radiation signal to the object being imaged and to detect reflections of such special radiation signal.